1. Field of the Invention
The present invention pertains to valves and methods of use thereof. Specifically, it pertains to fluid circulating valves particularly useful in well drilling operations for recovering lost equipment or freeing equipment which may be lodged within the well.
2. Description of the Prior Art
In the drilling and production of wells, particularly oil and gas wells, a portion of the drill string or tools, such as a drill bit, may become stuck or actually lost in the well bore. If a tool is twisted off or lost in the well bore, it then becomes necessary to perform what is sometimes called a "fishing" operation to retrieve the lost tool. A fishing string may comprise an overshot tool and possibly other tools such as drain subs, bumper jars, hydraulic or mechanical jars, drill collars, etc. connected to the lower end of a pipe string. The drain sub in a fishing string is required so that the pipe may drain as the lost object or "fish" is recovered from the hole. However, drain subs of the prior art do not allow washing operations which might be desirable to remove mud or other debris which has settled on the top of or around the lost tool.
Another problem associated with fishing operations is the assurance that the lost tool has been engaged by the overshot tool. With fishing methods and equipment of the prior art, particularly when the lost tool or fish is of small size and weight, the operator cannot determine if the lost tool has been engaged. On many occasions, it has been discovered, after pulling the fishing string out of the well bore, that the lost tool is still in the well bore.
In washover operations, a wash pipe with associated tools, such as a washover shoe, wash pipe bushing, safety joints, bumper jar, hydraulic or mechanical jars, drill collars, and the like, may be connected to the bottom of a pipe string which runs to the surface. The washover assembly is normally lowered to the lodged item so that the washover pipe surrounds the lodged item. Then, washing fluid is circulated through the pipe string in an attempt to wash away the mud or other debris which may be holding the stuck equipment in the well bore. However, the necessary large diameter of the wash pipe which is required to surround the lost drill pipe, drill collars, or other equipment, creates problems due to the small clearances between the well bore and the outside diameter of the wash pipe. This small clearance may cause pressure build-up as the pipe string is lowered into the well bore, increasing the time required for such operations and sometimes causing permanent damage to the formation surrounding the well bore. This small clearance also creates a problem when the pipe string is removed from the well bore since a partial vacuum may be created below the wash pipe creating a condition sometimes referred to as "swabbing" which may result in a well blowout.